function ajax(url, params, callback){
	this.url=url;
	this.params=params;
	this.req_obj=function(){
		if(window.XMLHttpRequest){
	              req=new XMLHttpRequest();
	        }else if(typeof ActiveXObject != 'undefined'){
	              req=new ActiveXObject('Microsoft.XMLHTTP');
	        }	
		return req;
	}

	this.req=this.req_obj();
		if(this.req){
			this.req.onreadystatechange=callback;
			this.req.open('POST', this.url, true)
                	this.req.setRequestHeader("Content-Type", "application/x-www-form-urlencoded")
                	this.req.send(params);
		}


}